Sweat It!

Prepping for a hot race day can help you run better in any weather.

You made it through a winter of hard training to prepare for a late spring or early summer race. The risk? Temps soaring on race day. Fortunately, there are ways to prepare for heat, even on short notice. The goal is to increase your volume of plasma, the liquid component of blood, so you can send blood to your skin to cool yourself without compromising the supply carrying oxygen to muscles. And if you're lucky and race day is cool, you'll still get a boost from these techniques.

Run hot. The best way to prepare for heat is to run for 60 to 90 minutes at an easy or moderate pace in conditions like the hottest you expect to face. You'll be acclimated after eight to 14 sessions, but those days don't have to be consecutive: You can space them as far apart as once every three days. If you can arrange a treadmill in a room at, say, 75 to 85 degrees, that's great. If the room isn't as warm as you'd like, wearing long sleeves and tights and avoiding the use of a fan can make an indoor run feel several degrees hotter than a comparable outdoor run.

Fitting in that many heat runs can be a challenge. A recent review found that three to seven heat adaptation runs produced a plasma volume increase of 3.5 percent on average—not as much as the seven percent gain from longer protocols, but still worthwhile.

Top up. Running in heat is an added stress, so you don't want acclimation to interfere with your taper. Heat adaptations last up to twice as long as you spend building them—so the effects of five heat-adaptation runs would last 10 days max. You can extend this with top-up sessions, adding one or two heat runs about a week before your race. For example, plan five heat runs in seven days starting three weeks before race day; do your hard workouts in cooler conditions on the other two days so you can hit your goal paces. Then consolidate your gains with two more top-up heat sessions six and eight days before the race.

Hydrate. Drink according to thirst during your heat runs. This will likely leave you mildly dehydrated, which may serve as an additional trigger for plasma expansion. Weigh yourself before and after to make sure you're not losing more than about two percent of your weight, then rehydrate immediately. Also, get some carbohydrate and protein within 10 minutes of finishing to maximize plasma gains.

Hit the sauna. Like many Finnish greats, four-time Olympic champion Lasse Viren swore by his postworkout sauna sessions. He may have been onto something: A 2007 study found that runners who took a postrun sauna for about 30 minutes at 194 degrees four times a week for three weeks boosted their plasma volume by seven percent and endurance by 1.9 percent. And this year, Australian scientists found that just four 30-minute postrun sauna sessions at 189 degrees increased plasma volume. To supplement heat runs, start with five to 10 minutes at 175 degrees and build up, and don't hit the sauna the same day as a heat run.

* * *

Alex Hutchinson is a former physicist and national-class runner, and a National Magazine Award-winning science journalist.

Advertising helps us deliver great running information and advice

Enter your email or disable your ad blocker to access all content on

Are you sure you want to log out?

If you are the only person using this device,
there’s no need to log out. Just exit this page
and you won’t have to sign in again. But if
you’re on a public or shared computer, log out
to keep your account secure.